An arrangement of the above kind is disclosed in U.S. Pat. No. 5,089,232.
In the known arrangement, channel-shaped recesses are worked into a carrier. These recesses hold respective color indicators and additional reaction partners for the colorimetric detection reaction. The reaction partners can be identical in each of the channels or they can be different depending upon whether a multiple detection of the same gas component is to be carried out or if a detection of different gas components in air is to be carried out. Each of the channels has at least one inlet opening for the toxic substance to be detected which is either drawn by suction through the channel or diffuses into the channel. Each individual channel thereby operates as a conventional individual testing tube for the colorimetric detection of gaseous components in air. A multiple measuring device in miniaturized form for the colorimetric detection of gaseous toxic substances is obtained with the arrangement of several channels arranged one parallel to the other on the carrier. The chip-shaped carrier is evaluated by an optoelectronic scanning apparatus. For this purpose, a transmitting and detecting unit is guided at the same elevation and in identical length to each of the individual channels and the light reflected from the colored channel zone is evaluated. The length of the coloration zone provides information as to the concentration contained in the detection sample or the quantity of the gaseous component to be investigated in dependence upon whether the channels are configured as testing tubes for throughflow or as dosimeters for diffusion of tile toxic substance.
In the known arrangement, the reaction zones are produced as channels in the base structure of the carrier material and they are in the form of recesses having a shallow depth. The subsequent coating of the channel recesses is possible only under difficult manufacturing conditions and produces an unsatisfactory result with respect to a uniform distribution of the reaction partners, especially of the color indicator along the entire length of the channel recesses. This is especially caused by introducing the reaction partners from a liquid emulsion so that a distribution of the reaction partner in a nonuniform density occurs within the channel because of surface tensions of the liquid and because of nonuniform distribution of the solid constituents in the suspension.
This situation is made still more critical when different reagent carriers for detecting various gaseous components are utilized in the different channels so that also different suspensions are used having different surface tensions and different solid reaction carriers with the solid reaction carriers being distributed in the suspension. A nonuniform distribution of the reaction partners along the channels can result in a fluctuation of the color indication which is not caused by the toxic substance to be detected and leads to the falsification of the measuring result.